This invention relates to engine covers, such as valve or rocker covers, and to their mounting on an engine for noise isolation and sealing.
It is known in the art relating to engine valve and rocker covers to provide a gasket and grommet mounting and noise isolation system which interrelates the sealing performance and noise isolation in provision of a robust cover design. Noise isolation is provided by mounting a cover with a grommet at each hold down bolt location and by a peripheral molded seal or gasket between the cover and the engine cylinder head or block which separates the cover from direct metal to metal contact. The forces required to seal the molded gasket may be unevenly applied because of variations in bolt pattern and spacing resulting in differing grommet loads and sealing variations at various locations around each part. Control of noise isolation may be compromised due to non-uniform compression sealing of the gasket, varying grommet loads and reaction distortions in the cover. An improved cover mounting system which separates the noise isolation and sealing functions is accordingly desired.
The present invention provides for mounting of a sealed cover, such as an engine valve or rocker cover. The cover is mounted on the engine with balanced grommets which support the cover through equal compression loads on inner and outer sides of the cover. Thus, a sealing surface of the cover is positioned with a fixed gap from a facing sealing surface of an associated engine component. The gap is sealed by a liquid RTV seal material that is vulcanized in place at room temperature after installation of the cover. The arrangement separates the function of noise isolation from the sealing function performed by the RTV material so that the specifications of the sealing material and the noise isolating grommet material can be varied as desired to perform their separate functions without a change in one affecting the other.
The grommet design is made such that it applies load equally to both inner and outer surfaces of the cover at its mounting holes. For this purpose, the grommet is formed with an equal mass of resilient material in inner and outer portions on opposite sides of the cover mounting opening. A through bolt and a height limiting sleeve are utilized to secure the cover and compress the grommet to a fixed dimension above the associated engine mounting surface. Since the compression of both portions of the grommet is equal, the center of the cover mounting opening is maintained with equal spacing between the compression members represented by the bolt head and the height limiting sleeve.
The design is such as to support the cover sealing surface with a fixed gap in opposition to the associated engine sealing surface so that the RTV sealing material which is put in place prior to mounting the cover on the engine is maintained in position without any compression load applied by the cover against the RTV seal. Since there is no cover load on the seal, the seal does not apply any reaction load against the cover and therefore there is no distortion of the cover or the noise isolation grommets that would result in changing the loading of the seal or the isolating functions of the grommets. Accordingly, the stiffness or isolating characteristics of the grommets may be altered for improved noise isolation without having any effect on the RTV seal material. Also, the seal material and the gap in which the material is located may be altered in design variations in order to provide a more effective seal without having any effect on the noise isolation characteristics of the grommets.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.